1. Field of the Invention
This invention pertains to a process for supplemental oil recovery, and more particularly it pertains to an improved surfactant water flooding supplemental oil recovery process. Still more particularly, this invention pertains to a surfactant water flooding supplemental oil recovery process employing at least two distinct surfactant fluids, the first fluid injected into the formation containing an emulsifying surfactant and the second fluid containing a surfactant which produces a minimum interfacial tension between the aqueous fluid and the formation petroleum, and which produces essentially no emulsion.
2. Background of the Invention
It is well recognized by persons skilled in the art of oil recovery techniques that only a fraction of the amount of oil or petroleum originally present in a petroleum reservoir can be recovered by primary production, e.g., by allowing the oil to flow to the surface of the earth as a consequence of naturally occuring energy forces, or by so called secondary recovery which comprises injecting water into a formation by one or more wells to displace petroleum toward one or more spaced-apart production wells, from which it is recovered to the surface of the earth. Although water flooding is an inexpensive supplemental oil recovery process, water does not displace oil effectively even in those portions of the formation through which it passes, because water and oil are immiscible and the interfacial tension between water and oil is quite high. This too has been recognized by persons skilled in the art of oil recovery, and many surface active agents or surfactants have been proposed for incorporation in the water flood for the purpose of reducing the interfacial tension between the injected aqueous fluid and the formation petroleum, thereby recovering substantially more of the petroleum present in the portion of the formation through which the injected aqueous fluid passes than is possible for simple water flooding alone. Petroleum sulfonate has been utilized for this purpose, and many references in the prior art disclose the use of petroleum sulfonate. Petroleum sulfonate, however, suffers from a serious limitation, namely that it is not effective in the presence of relatively high salinity water, e.g., water whose salinity exceeds about 20,000 parts per million total dissolved solids, and so other types of surfactants must be employed if the surfactant will contact water having salinities greater than the above stated figure.
A particularly promising surfactant for use in oil recovery processes involving surfactant water flooding is an alkyl- or alkylarylpolyalkoxy (usually polyethoxy) alkyl sulfonate. The surfactant can be utilized in the presence of very high salinity brines, up to at least 240,000 parts per million total dissolved solids, and additionally can be employed safely in formations having relatively high temperatures, e.g., as high as 250.degree. F. (121.1.degree. C.). The use of alkyl- or alkylarylpolyalkoxylalkyl sulfonates in surfactant water flooding processes is described in the following U.S. Pat. Nos.: 3,827,497-Dycus et al; 3,890,239-Dycus et al; 3,977,471-Gale et al; and 4,018,278-Shupe.
Despite the existance of a substantial amount of prior art describing the use of surfactant water flooding oil recovery processes for recovering increased amounts of petroleum from subterranean formations over that recoverable by the use of water flooding alone, little commercial use has been made of surfactant water flooding processes because the amount of additional petroleum recovered thereby has not been sufficient to justify the high cost of surfactants necessary for use in these processes.
In view of the foregoing discussion, and particularly in view of the serious current shortage of petroleum, it can be appreciated that there is a significant need for a supplemental oil recovery process by means of which increased amounts of petroleum may be obtained from the known petroleum formations. More specifically, there is a substantial need for an improved surfactant water flooding supplemental oil recovery process which will recover significantly greater amounts of petroleum while employing an economically acceptable amount of surfactant.